Photothermal Actuation Research Articles

Self-Cleaning MXene/Bacterial Cellulose Composite Film for Photothermal Actuation and Sterilization

Self-Cleaning MXene/Bacterial Cellulose Composite Film for Photothermal Actuation and Sterilization

Imidazole-stabilized gold nanoclusters as photocatalytic initiator and crosslinker to fabricate functional hydrogel

Photopolymerization is the most widely used method to fabricate hydrogels, which hold great potentials in various fields including biomedical applications, electronic skin and flexible wearable devices. Herein, gold nanoclusters (AuNCs) were employed as both efficient photo-initiators and crosslinkers to prepare polyacrylamide (PAM) hydrogels with good mechanical properties. Firstly, an imidazole-based monomer, ImPAA, was designed and synthesized, serving as an reducing agent and ligand to prepare imidazole-stabilized AuNCs (AuNC@ImPAA) in water. Under white light irradiation, AuNC@ImPAA efficiently initiated the radical polymerization of acrylamide monomers in water via a photocatalytic mechanism. The abundant vinyl groups on the surface of AuNC@ImPAA enabled its role as a multiple covalent crosslinker, endowing the resulting hydrogel with impressive mechanical properties. The maximum tensile strength and fracture strain was 287 kPa and 591 %, respectively. Moreover, triggered by UV light, the embedded AuNC@ImPAA within the hydrogel aggregated and converted into gold nanoparticles (AuNPs), yielding an AuNP/PAM hydrogel. This hybrid AuNP/PAM hydrogel exhibited a good photothermal conversion performance, with an efficiency of 14.14 % under 660 nm laser irradiation, and its potential as a photothermal actuator was demonstrated. Thus, we provide a facile light-mediated strategy to fabricate functional hydrogel.

3D printed Ti3C2@Polymer based artificial forest for autonomous water harvesting system

The escalating scarcity of freshwater resources presents significant challenges to global sustainability, demanding innovative solutions by integrating cutting-edge materials and technologies. Here we introduce an autonomous artificial forest (3D AF) for continuous freshwater acquisition. This system features a three-dimensional (3D) architecture incorporating a carbon nanofiber (CNF) network and MXene@polypyrrole (Ti3C2@PPy), enhancing surface area, light absorption, heat distribution, and surface wettability to improve solar vapor generation and fog collection efficiency. The autonomous operation is facilitated by an integrated photothermal actuator that adjusts to the day and night conditions. During daylight, the 3D AF tilts downward to maximize solar exposure for water evaporation, while at night, it self-adjusts to optimize fog particle collection. Notably, our device demonstrates the ability to harvest over 5.5 L m−2 of freshwater daily outdoors. This study showcases the potential of integrating advanced materials and technologies to address pressing global freshwater challenges, paving the way for future innovations in water harvesting.

A Light-Driven Carbon Nanocoil Microrobot

Mobile microrobots are of great scientific significance. However, external actuation and control methods are still challenging to conduct. We present a single carbon nanocoil (CNC) microrobot induced by an NIR laser beam, capable of light-driven locomotion and photothermal actuation. This research demonstrates that CNC-based microrobots rolls away from the focal spot when the laser beam is focused near the CNC. The maximum translational distance of a CNC microrobot increases with an increase in laser power, and the direction of motion is guided by controlling the focusing position of NIR. CNC-based microrobots can load and transport multiple cells under NIR light irradiation, resulting from the temperature gradient generated by photothermal conversion, which causes thermophoresis. The hydrophobic surface and unique helical structure of CNCs are beneficial to the underwater drag reduction in CNC microrobots’ motion and the adhesion of cells on CNC microrobots. Therefore, CNC microrobots, as cell vectors driven by a laser beam, may find applications in a wide range of biomedical applications. In addition, the rotation of a CNC powered by a laser beam provides promising prospects for the future of nanomechanical devices using a carbon nanocoil as a micro/nanomotor.

3D-Printed Hydrogels as Photothermal Actuators.

Thermoresponsive hydrogels were 3D-printed with embedded gold nanorods (GNRs), which enable shape change through photothermal heating. GNRs were functionalized with bovine serum albumin and mixed with a photosensitizer and poly(N-isopropylacrylamide) (PNIPAAm) macromer, forming an ink for 3D printing by direct ink writing. A macromer-based approach was chosen to provide good microstructural homogeneity and optical transparency of the unloaded hydrogel in its swollen state. The ink was printed into an acetylated gelatin hydrogel support matrix to prevent the spreading of the low-viscosity ink and provide mechanical stability during printing and concurrent photocrosslinking. Acetylated gelatin hydrogel was introduced because it allows for melting and removal of the support structure below the transition temperature of the crosslinked PNIPAAm structure. Convective and photothermal heating were compared, which both triggered the phase transition of PNIPAAm and induced reversible shrinkage of the hydrogel-GNR composite for a range of GNR loadings. During reswelling after photothermal heating, some structures formed an internally buckled state, where minor mechanical agitation recovered the unbuckled structure. The BSA-GNRs did not leach out of the structure during multiple cycles of shrinkage and reswelling. This work demonstrates the promise of 3D-printed, photoresponsive structures as hydrogel actuators.

Design of membrane-based microfluidic chip device based on bionic leaf and adsorption detection of tetracycline antibiotics by specific gel membrane

In this study, we developed copper alginate-carbon nanotube/copper sulfide-graphene oxide gel membranes based on the design inspired by the surface structure of leaves and plant transpiration in nature and through the modulation of high-density polymer networks. This light-driven water evaporation-specific adsorption gel membrane is capable of using solar energy to drive water evaporation from contaminated surface water to access tetracycline antibiotics for detection. Combined with the designed biomimetic adsorption detection chip, in situ monitoring of tetracycline antibiotics in water bodies was achieved. Compared with the traditional mass spectrometry detection method, it shows more outstanding performance in terms of time, environmental protection and technology. The microscale adsorption mechanism was further explored on the molecular scale by density functional theory (DFT). The results showed that tetracycline antibiotics were adsorbed on the aerogel membrane mainly through π-πEDA interactions in sandwich (S) configuration and parallel displacement (PD) configuration, which ensured high adsorption efficiency. Under the optimized conditions, the tetracycline concentration detected by the sensor showed a good linear relationship with the cyclic voltammetry curve, and the lowest detection limit was 1.59*10−4 μM. This adsorption detection strategy can reduce the influence of organic matter, inorganic matter, and other classes of antibiotics on the detection of tetracycline antibiotics, and provide a new idea for the high-efficiency photo-thermal actuation and in-situ testing of tetracycline antibiotics.

Asymmetric nanofiber photothermal interactive electronic skin with triboelectric autonomous thermal perceptivity

Thermal-perceptive electronic skins (e-skin) represent an important functional interface in wearables and soft robots. Realizing an all-in-one structured nanofiber interactive e-skin with autonomous thermal perceptivity remains challenging. We demonstrated a polyurethane/(polyvinyl pyrrolidone/MXene) (PPM) bilayer nanofiber film with asymmetric structure compactness by continuous and controllable electrospinning, that achieves asymmetric optical transmittance (visible light transparency of 20∼97%, infrared transparency of 5.5∼34.1%) and photothermal actuation response, with a response rate of 0.8 mm−1 s−1 and bending curvature of 2.2 cm−1, as well as additional excellent triboelectric outputs of ∼320 V and ∼5.4 µA. We proposed a “contact-actuation-perception” strategy for instantaneous object temperature sensing based on the PPM, which can actuate under photothermal stimulation to change its contact area with the target objects at different temperatures, producing temperature-dependent distinguishable triboelectric signals for autonomous thermal perception, with sensitivity up to ∼99.6%. This work could inspire a facile strategy to realize asymmetric features in fiber materials, in which the asymmetric optical-thermal-mechanical-electrical coupling mechanism for active perception is expected to promote the development of autonomous interactive e-skins.

Localized flow control by photothermal actuation of pNIPAAm hydrogel brushes in a macroporous silicon membrane

Localized flow control by photothermal actuation of pNIPAAm hydrogel brushes in a macroporous silicon membrane

All-optical driven soft crawler with complex motion capabilities

ABSTRACT The emergence of millimeter-scale soft actuators has significantly expanded the potential applications in areas such as search and rescue, drug delivery, and human assistance, due to their high flexibility. Despite these advancements, achieving precise control over the intricate movements of soft crawlers poses a significant challenge. In this study, we have developed an all-optical approach that enables manipulation of propulsive forces by simultaneously modifying the magnitude and direction of friction forces, thereby enabling complex motions of soft actuators. Importantly, the approach is not constrained by specific actuator shapes, and theoretically, any elongated photothermal actuator can be employed. The actuator was designed with an isosceles trapezoid shape, featuring a top width of 2 mm, a bottom width of 4 mm, and a length of 8 mm. Through our manipulation approach, we showcase a proof-of-concept for complex soft robotic motions, including crawling (achieving speeds of up to 2.25 body lengths per minute), turning, avoiding obstacles, handling and transferring objects approximately twice its own weight, and navigating narrow spaces along programmed paths. Our results showcase this all-optical manipulation approach as a promising, yet unexplored tool for the precision and wireless control for the development of advanced soft actuators.

Photothermal Performance of Lignin-Based Nanospheres and Their Applications in Water Surface Actuators.

In this study, the photothermal performance of lignin-based nanospheres was investigated. Subsequently, a photothermal actuator was prepared using lignin-based carbon nanospheres (LCNSs). The results demonstrated that LCNSs exhibited an impressive photothermal conversion efficiency of up to 83.8%. This extreme efficiency significantly surpasses that of lignin nanospheres (LNSs) and covalently stabilized LNSs (HT-LNSs). As a structural material, a hydrophobic coating was effectively engineered by LCNSs on the filter paper, achieving a water contact angle of 151.9° ± 4.6°, while maintaining excellent photothermal effects (with a temperature increment from room temperature to 138 °C in 2 s). When employing hydrophobic filter paper as the substrate for the photothermaldriven actuator, under the influence of a 1.0 W/cm2 power-density NIR laser, the material exhibited outstanding photothermal actuation, achieving speeds up to 16.4 mm/s. In addition, the direction of motion of the actuator can be adjusted in accordance with the location of the NIR light irradiation. This study offers valuable perspectives on the application of LNSs for highvalue applications and the development of innovative photothermal-driven actuators.

Photothermal Actuation of Thick 3D-Printed Liquid Crystalline Elastomer Nanocomposites.

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials that transduce an input energy into a mechanical response. LCE composites prepared with photothermal agents, such as nanoinclusions, are a means to realize wireless, remote, and local control of deformation with light. Amongst photothermal agents, gold nanorods (AuNRs) are highly efficient converters when the irradiation wavelength matches the longitudinal surface plasmon resonance (LSPR) of the AuNRs. However, AuNR aggregation broadens the LSPR which also reduces photothermal efficiency. Here, the surface chemistry of AuNRs is engineered via a well-controlled two-step ligand exchange with a monofunctional poly(ethylene glycol) (PEG) thiol that greatly improves the dispersion of AuNRs in LCEs. Accordingly, LCE-AuNR nanocomposites with very low PEG-AuNR content (0.01wt%) prepared by 3D printing are shown to be highly efficient photothermal actuators with rapid response (>60%strains-1) upon irradiation with near-infrared (NIR; 808nm) light. Because of the excellent dispersion of PEG-AuNR within the LCE, unabsorbed NIR light transmits through the nanocomposites and can actuate a series of samples. Further, the dispersion also allows for the optical deformation of millimeter-thick 3D printed structures without sacrificing actuation speed. The realization of well-dispersed nanoinclusions to maximize the stimulus-response of LCEs can benefit functional implementation in soft robotics or medical devices.

Photothermal porous monodomain liquid crystal elastomer actuator based on confined expansion method

Light-driven monodomain liquid crystal elastomers (mLCEs) have the advantages of remote operation and local control, but the response time will increase rapidly with the increase of thickness due to the limitation of the incident light depth. In order to achieve fast response, porous AuNPs-mLCEs actuators are proposed and fabricated by a confined expansion method. The average pore size of the prepared rod-shaped porous mLCEs is 200 μm, the porosity is 46.5%, and the order parameter of mesogens is 0.41. When the diameter is 3 mm, the response time is 1.2 s at a wavelength of 532 nm and a light intensity of 2.6 W•cm−2. When the diameter increases to 10 mm, the response time only increases to 2.2 s. The contraction of porous mLCEs actuator caused by the photothermal effect enables it can not only to lift an object 321.5 times heavier than itself by contraction, but also raise-up an object 5.2 times heavier than itself by bending. This method can be used to design and manufacture various 3D porous photothermal actuators with fast response.

Fabrication and Photothermal Actuation Performances of Electrospun Carbon Nanotube/Liquid Crystal Elastomer Blend Yarn Actuators.

Liquid crystal elastomers (LCEs) are a kind of polymer network that combines the entropic elasticity of polymer networks and the mesogenic unit by means of mild cross-linking. LCEs have been extensively investigated in various fields, including artificial muscles, actuators, and microrobots. However, LCEs are characterized by the poor mechanical properties of the light polymers themselves. In this study, we propose to prepare a carbon nanotube/liquid crystal elastomer (CNT/LCE) composite yarn by electrospinning technology and a two-step cross-linking strategy. The CNT/LCE composite yarn exhibits a reversible shrinkage ratio of nearly 70%, a tensile strength of 16.45 MPa, and a relatively sensitive response speed of ∼3 s, enabling a fast response by photothermal actuation. The research disclosed in this article may provide new insights for the development of artificial muscles and next-generation smart robots.

Photothermal Conversion of the Oleophilic PVDF/Ti3C2Tx Porous Foam Enables Non-Aqueous Liquid System Applicable Actuator.

Various physical and chemical reaction processes occur in non-aqueous liquid systems, particularly in oil phase systems. Therefore, achieving efficient, accurate, controllable, and cost-effective movement and transfer of substances in the oil phase is crucial. Liquid-phase photothermal actuators (LPAs) are commonly used for material transport in liquid-phase systems due to their remote operability and precise control. However, existing LPAs typically rely on materials like hydrogels and flexible polymers, commonly unsuitable for non-aqueous liquids. Herein, a 3D porous poly(vinylidene fluoride)(PVDF)/Ti3C2Tx actuator is developed using a solvent displacement method. It demonstrates directional movement and controlled material transport in non-aqueous liquid systems. When subject to infrared light irradiation (2.0Wcm-2), the actuator achieves motion velocities of 7.3 and 6mms-1 vertically and horizontally, respectively. The actuator's controllable motion capability is primarily attributed to the foam's oil-wettable properties, 3D porous oil transport network, and the excellent photothermal conversion performance of Ti3C2Tx, facilitating thermal diffusion and the Marangoni effect. Apart from multidimensional directions, the actuator enables material delivery and obstacle avoidance by transporting and releasing target objects to a predetermined position. Hence, the developed controllable actuator offers a viable solution for effective motion control and material handling in non-aqueous liquid environments.

Nanoscale Rheology: Dynamic Mechanical Analysis over a Broad and Continuous Frequency Range Using Photothermal Actuation Atomic Force Microscopy.

Polymeric materials are widely used in industries ranging from automotive to biomedical. Their mechanical properties play a crucial role in their application and function and arise from the nanoscale structures and interactions of their constitutive polymer molecules. Polymeric materials behave viscoelastically, i.e., their mechanical responses depend on the time scale of the measurements; quantifying these time-dependent rheological properties at the nanoscale is relevant to develop, for example, accurate models and simulations of those materials, which are needed for advanced industrial applications. In this paper, an atomic force microscopy (AFM) method based on the photothermal actuation of an AFM cantilever is developed to quantify the nanoscale loss tangent, storage modulus, and loss modulus of polymeric materials. The method is then validated on styrene-butadiene rubber (SBR), demonstrating the method's ability to quantify nanoscale viscoelasticity over a continuous frequency range up to 5 orders of magnitude (0.2-20,200 Hz). Furthermore, this method is combined with AFM viscoelastic mapping obtained with amplitude modulation-frequency modulation (AM-FM) AFM, enabling the extension of viscoelastic quantification over an even broader frequency range and demonstrating that the novel technique synergizes with preexisting AFM techniques for quantitative measurement of viscoelastic properties. The method presented here introduces a way to characterize the viscoelasticity of polymeric materials and soft and biological matter in general at the nanoscale for any application.

Design and mechanism of photothermal soft actuators and their applications

This article discusses the fundamentals and progress of photothermal actuators, and their applications from bionic design to intelligent robots in detail.

Tendril‐Inspired Programmable Liquid Metal Photothermal Actuators for Soft Robots

AbstractPhotothermal actuators are widely applied in robots, smart devices, and bionic systems. However, asymmetric thermal expansion, the most common mechanism for preparing photothermal actuators, has not been utilized in programmable liquid metal photothermal actuators. In this work, Liquid metal/Polyimide/Polytetrafluoroethylene (LM/PI/PTFE) programmable photothermal actuators based on asymmetric thermal expansion are prepared inspired by the climbing plant tendrils. The “protoplasm that can contract and bend” PTFE tape endows the photothermal actuator with programmable initial morphology. The photothermal properties and flexibility of the liquid metal microspheres, together with the significant property difference between PI and PTFE, endow the photothermal actuator with excellent response angles (130.74 ± 6.45°), response speeds (46.62 ± 2.33° s−1), stability (2000 cycles for 10 h), and load‐carrying capacity, which are not inferior to most of the reported PI photothermal actuators. The LM/PI/PTFE photothermal actuator has been successfully modelled and simulated by finite element analysis (FEA). Based on the programmable initial morphology and the simulation by FEA, this work has designed and prepared a variety of bionic systems and functional robots. The work of LM/PI/PTFE photothermal actuators provides a strategy for designing photothermal actuators and enables the future development of photothermal actuators in bionic systems and robots.

Reprogrammable 4D Printed Liquid Crystal Elastomer Photoactuators by Means of Light‐Reversible Perylene Diimide Radicals

AbstractReconfigurable soft actuators can be programmed to morph into different 3D shapes under the same stimulus exhibiting great potential for adaptive robotic functionalities. Liquid crystalline crosslinked materials programmed and controlled by light have demonstrated great potential in this area, however, their implementation is mainly based on azobenzene chromophores, using ultraviolet light that can potentially damage the device and its surroundings, especially if living cells are present. Here, an ink is presented, containing a green‐absorbing perylene diimide chromophore, to prepare light active liquid crystalline elastomer (LCE) actuators via direct ink writing. Green light irradiation of the LCE elements leads to photothermal actuation, but also to new absorption bands in the far‐red and near‐infrared, ascribed to the formation of radical species. Far‐red irradiation results in mechanical actuation and, advantageously, a recovery of the original absorption spectrum. This reversible transformation enables spatial reconfigurability of the actuator's response to far‐red light. The reconfigurable system gives access to complex deformation modes by simply exciting the element with homogeneous far‐red light, without the need for any structural modification of the actuator. This material strategy, using green and far‐red light, less harmful than ultraviolet, shows significant promise for future development of reconfigurable actuators for biomedical applications.

Switchable photothermal conversion efficiency for reprogrammable actuation

Reprogrammable soft matter brings flexibility to soft robots so that they can display various motions, which is flourishing in soft robotics. However, the reprogramming of photoresponsive materials used in soft robots is time-consuming using existing methods. In this study, we promote a strategy for rapid reprogramming via switchable photothermal conversion efficiency (PCE). The liquid crystalline elastomers doped with semiconductor bismuth compounds (Bi-LCE) used in this work exhibited large photothermal actuation with over 35% shrinkage in 5 s at high PCE state, which demonstrated little deformation at low PCE state. Furthermore, the material was capable of being reprogrammed up to 10 times, with only 20 min required for one PCE reversible switch. Based on this switchable PCE effect, the same Bi-LCE film displayed various shape changes through different programmable pattern. Additionally, a reprogrammable hollow tube made of PCE reprogrammable materials could tune the diameter, cross-section configuration, and surface morphology, which was crucial for microfluidics field. Reprogrammable materials provide endless possibilities for reusability and sustainability in robotics.

Polydopamine-Modified MXene-Integrated Poly(N-isopropylacrylamide) to Construct Ultrafast Photoresponsive Bilayer Hydrogel Actuators with Smart Adhesion.

In nature, living organisms, such as octopuses, cabrito, and frogs, have already evolved admirable adhesive abilities for better movement and predation in response to the surroundings. Inspired by biological structures, researchers have made enormous efforts in developing actuators that can respond to external stimuli, while such adhesive property is very desired, yet there is still limited research in responsive hydrogel actuators. Here, a bilayer actuator with high stretchability and robust interface bonding is presented, which has a smart adhesion and thermoreception function. The system consists of an adhesive passive layer copolymerized of amphoteric ([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl), SBMA) and acrylic acid (AA), and an active layer hydrogel composed of poly(N-isopropylacrylamide) (PNIPAm) containing polydopamine-modified MXene (P-MXene) and calcium chloride (CaCl2). The coordination of carboxylate and Ca2+ at the interface of the two layers enhances the interfacial bonding from 14 to 30 N m-1, which facilitates withstanding large strain and preventing stratification. The resulting hydrogel actuator can bend approximately 360° in a mere 10 s, exhibiting excellent photothermal effect, a large angle bending deformation, and ultrafast photoresponsive ability. As a proof of concept, the photothermal actuators are programmed to present various shapes and grab objects. Importantly, the hydrogel actuator exhibits remarkable adhesion capabilities toward diverse substrates, with a maximum peel force of up to 280 N m-1. Relying on their own adhesion and the photoresponse properties, these flexible adhesion actuators show outstanding gripping capability, enabling them to grip and release objects of different shapes and weights. More interestingly, the hydrogel exhibits a smart adjustable adhesion capability at different temperatures, which enables it as a gripper to recognize temperature signals through real-time different feedback actions based on its own adhesion. This study presents innovative insights into biomimetic hydrogel actuators, providing new opportunities for developing intelligent soft robots with multiple functions.